ATOMISATION OF LIQUIDS

Abstract: The invention relates to the atomisation of liquids. There are many fields of application where a spray, mist, or jet of fine droplets is required and where control over droplet size is important. Of particular significance is the medical field and the nebulising of drug to be administered to a patient by the inhaled route, where the deposition of the drug and its efficacy is a direct function of the droplet size. The object of the invention is to improve the control over droplet size, an objective met by a method and a construction where liquid is centrifugally forced through an orifice sized to generate a droplet (27) of the liquid of a required size. Thus, the liquid maybe introduced into a drum (14) with sized holes (26) or pores in its wall or into a rotor formed by plates (1,2) secured together with a spacing to provide an annular orifice (4) of a required size, the rotation of the drum (14) or rotor causing the forcing of the liquid through the holes (26) or pores, or through the orifice (4), the centrifugal force and the Bernoulli effect causing the liquid to issue in the form of droplets (27) of a predetermined size.

Description: ATOMISATION OF LIQUIDS This invention relates to the atomisation of liquids. There are many fields of application where a spray, mist or jet of fine droplets of liquid are required, and where control over droplet size is of paramount importance. Thus, in fuel technology there is the injection of liquid fuel into burners, and the injection of liquid fuels into combustion chambers of engines. In materials technology there is the spraying of metals and plastics material to provide specialised coatings. Atomising of liquid metal is also employed in the production of metal powders of controlled particle size. A particularly significant usage of atomised liquids is in the medical field, for the administration of required drugs to, such as, the bronchial tree or the alveoli of the lungs of a patient. Here it is well-known to employ a drug in liquid soluble form, and for the drug to be nebulised and administered via the inhaled route. To facilitate this nebulisers already exist and broadly fall into two categories, the first where compressed air or other inhalable gas is used to drive the liquid through a small orifice to nebulise the liquid by a venturi effect, and the second where nebulising is effected by ultrasonic vibration. Nebulisers of the first category are relatively inefficient. The deposition of the drug at its required site and its efficacy is a direct function of the droplet size of the nebulised liquid, and with compressed-air-driven nebulisers it is virtually impossible for there to be any control over droplet size, the droplets are non-uniform with a wide range of sizes, and as a direct consequence only a small proportion of the drug is deposited at the intended site. Nebulisers of the second category rely on high frequency sound waves focussed on the surface of the liquid to be nebulised. The sound waves are created by the vibration of a piezo-electrical crystal. Here again control over droplet size is limited and with the same result that only a proportion of the drug administered is effectively deposited at the intended site. With nebulisers of either category they are generally operated by either mains supply or by relatively substantial rechargeable batteries, and consequently in addition to having inefficient control over droplet sizes, with then but a proportion of the drug being effectively deposited at its required site, they additionally have the disadvantage of being bulky, heavy and relatively expensive. It is the object of the present invention to provide a means of atomising liquids with considerable control over droplet size. According to a first aspect of the present invention, a method of providing an atomised liquid comprises the centrifugal forcing of liquid through one or more small orifices sized to generate a droplet of the liquid of a required size. According to a second aspect of the present invention, an atomiser for liquids comprises a means of containing a liquid, a means associated therewith and having at least one hole therethrough of a predetermined size and there being a further means associated therewith to cause the centrifugal forcing of liquid through the at least one hole. According to a third aspect of the present invention, an atomiser for liquids comprises a drum rotatably mounted within a housing, a drive means for rotating the drum, at least one hole through the wall of the drum and an inlet to and an outlet from the housing. The method and the atomiser above defined are capable of industrial use, but are particularly suited for use as a medical nebuliser to provide a nebulised aerosol. Preferably, the drive means for the drum is a small battery-driven electric motor such as are already known and capable of running at very high rates of revolution. Further preferably, said electric motor and battery are contained in their own housing that may be attached to, or formed integral with, the drum housing, with a drive shaft from the motor extending to the drum. The outlet from the drum housing is preferably formed with a mouthpiece of a shape suited to be placed within the mouth of a patient. Preferably, an inlet to the housing is provided that may be an opening strategically located in the housing wall, but could equally be provided by forming the drum housing from an air permeable material. The at least one hole in the wall of the drum is critical to the formation of droplets of a required size, and is of a diameter smaller than the diameter of the droplet to be formed. On the one hand there is the drug in its liquid form with its surface tension, and there is the Bernoulli effect on droplet formation of liquid passing through an orifice. In additiion, there is the intended deposition site within the patient and where a different droplet size will provide for the more efficient depositing of the nebulised liquid drug at its required site. From these parameters it is then possible to predetermine a hole size required in the drum that would suit a particular liquid drug and the intended deposit site in the patient. It will be understood that the diameter of said hole or holes will be very small but able to be produced, such as by laser cutting or spark erosion techniques, or such as by embedding exceedingly fine filamental material in the wall of the drum during its manufacture of a different melting point or solubility to the material of the drum and when heating of the drum or the treatment of the drum with a solvent allows the melting out, vaporisation, or dissolving of the filamental material to leave one, or a required number, of transverse holes through the wall of the. drum, of the required diameter. Equally the drum may be formed from a micro-porous, synthetic plastics material, or from a micro-porous polymer material. Thus, with a liquid drug placed within the drum, the mouthpiece/outlet from the housing can be placed in a patient's mouth and the motor activated by such as simple switch means, externally of the motor housing, and when the drum is rotated at a high rate and at an angular velocity to overcome the Bernoulli effect and the surface tension of the liquid, with the direct result that droplets of the liquid drug are formed as the liquid passes through the or each hole of predetermined size in the wall of the drum, with the guarantee that the droplets are predominantly of the required size to suit the drug and to suit the intended site within the patient. With the mouthpiece or outlet from the housing in the patient's mouth the patient has to do no more than breathe normally to ensure the effective deposit of the nebulised liquid drug within the bronchial system or the lungs. To enable the liquid drug to be placed within the drum, the drum housing may be removable- to expose the drum and a closable opening may be provided in the drum. Alternatively, a closable opening may be provided in the housing to allow access to a closable opening in the drum. Alternatively, the drum housing may additionally serve as a container for the liquid drug, with an appropriate means provided to transport the drug from within the drum housing to within the drum. Such a construction has the advantage that if, and during use, there is the gathering of droplets on the wall of the drum housing, they drain back to the position of the bulk of liquid for subsequent feeding to the drum. According to a fourth aspect of the present invention, an atomiser for liquids comprises a rotor, passageway means through the rotor terminating in orifice means at the periphery of the rotor, means to supply liquid to the passageway means, drive means for the rotor and means to enable droplets of liquid emerging from the orifice means to be entrained in a gas flow. Preferably, the rotor is formed by plate members suitably secured together, the inner surfaces of the plate members being structured such as to provide the passageways and the associated outlet orifices, the spacing between the plates determining the size of the orifices, and enabling considerable control over orifice size down to very small orifices of the order of less than 10 microns. The means of enabling formed droplets of liquid to be entrained in a gas flow may be by providing a gas chamber in which the rotor is mounted, with a gas inlet and gas outlet to the chamber. The supply of liquid to the rotor may be by way of a supply line located centrally of the rotor and extending to an appropriate source of liquid supply and there may be pump or other suitable means to cause the supply of liquid to the rotor. Conveniently, however, the air chamber may also serve as a sump to contain liquid, and the supply line extend from the rotor to liquid contained in the sump. The drive means for the rotor may be an electric motor, mains driven, and may be a small battery driven motor. Conveniently, the motor may be mounted on the air chamber with a drive shaft extending into the chamber and to the rotor. In its forms of construction suited to industrial use, a source of compressed gas may be connected to the gas chamber, and a supply line or outlet nozzle connected to the outlet from the gas chamber. In its forms of construction suited to medical use, a mouthpiece may be secured to the outlet from the gas chamber. and a filter means provided at the inlet to the chamber, enabling a patient to inhale air drawn through the chamber, with droplets of nebulisable drug entrained in the air. In all of its forms of construction and uses, it is the careful selection of an orifice size to suit the liquid and the end usage, and the careful selection of a rotor diameter and its angular velocity of rotation that enables the production of uniform droplets of liquid of required size, with the additional benefit that for any given orifice size and rotor diameter, the droplet size can be adjusted by varying the angular velocity of the drum. Two embodiments of the invention suited to use as a medical nebuliser will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 shows a longitudinal section of a first embodiment of medical nebuliser in accordance with the invention; Figure 2 is an enlarged section of the rim section of the rotor of Figure 1; Figure 3 is a longitudinal section of a second embodiment of medical nebuliser in accordance with the invention; and Figure 4 is an enlarged view of part of the drum of Figure 3. In Figures 1 and 2 of the drawings a rotor is formed by two conical plates 1 and 2 suitably secured together to form a passageway 3 and a restricted orifice 4. The conical rotor so formed is driven by a direct current electric motor 5 but in many applications an induction motor may be employed to minimise vibration and starting torque. The plate 2 has a feed pipe 3A extending below the surface of a liquid to be atomised (nebulised) that is held in a sump 6 that also serves as an air chamber 6A to feed the rotor by capillary action or by way of a helical groove machined in the feed pipe. The motor is secured by a resilient mounting 7 to a housing 8 on the air chamber/sump to minimise vibration and optimise motor speed. The motor 5 is powered by a direct current source 9 and activated by a switch 10. A current limiting device may be required for smooth starting of the motor and to allow gradual attainment of operating speed. The atomised (nebulised) aerosol is contained in the sump 6 of the air chamber 6A. Air can be entrained through an inlet 11 which may be fitted as shown here with a filter 12 to prevent the ingress of particulate matter, and the aerosol inhaled by the patient through a mouthpiece 13 at the outlet from the air chamber. In the. example of a medical nebuliser shown, the orifice 4 is less than 10 microns and the required angular velocity of the motor 5 is of the order of 10,000 to 40,000 r.p.m. The sloping sides of the air chamber 6A ensures that any condensing or coalescing of the drug on it would be returned to the sump 6 and recirculated. In Figures 3 and 4 of the drawings, a drum 14 is driven by a direct current electric motor 15. The motor 15 is secured by a flexible base plate 16 to a housing 17, to minimise vibration, and to optimise motor speed, and there being within the housing 17 a power source, e.g. a battery 18, for the motor. The motor 15 is connected by a drive shaft 19 to the drum 14, and the drum is located in a chamber 20 to which the housing 17 is secured. A capillary tube 21 is provided extending from the bottom of the chamber 20 and into the drum 14. To one side of the chamber is an inlet 22 across which a filter 23 is provided, and to the opposite side of the chamber there is an outlet 24 to serve as a mouthpiece 25 or to which a mouthpiece can be attached. In the wall of the drum a number of extremely fine holes or passageways 26 are provided, sized to generate droplets of liquid of a required size to suit a particular drug being used and the intended deposition site within a patient. Thus, with an appropriate liquid drug placed in the chamber 20, and the motor activated to rotate the drum, liquid drug rises up. the capillary tube and into the drum, and is urged by centrifugal force against the inner wall of the drum. Liquid drug is forced through the fine holes 26 with a Bernoulli effect on the liquid as it emerges through the hole to cause the creation of droplets 27. With the patient inhaling air through the mouthpiece 25, air is drawn through the chamber from the inlet 22, in which the droplets 27 are entrained, and drawn into the patient along with the inhaled air. Any droplets not passing through the outlet fall back into the volume of liquid in the chamber, to be carried back into the drum through the capillary tube.

Claims: CLAIMS 1. A method of providing an atomised liquid comprising the centrifugal forcing of a liquid through one or more small orifices sized to generate a droplet of the liquid of a required size. 2. An atomiser for liquids comprising a means of containing a liquid, a means associated therewith, and having at least one hole therethrough of a predetermined size and there being a further means associated therewith to cause the centrifugal forcing of liquid through the at least one hole. 3. An atomiser as in Claim 2, comprising a drum rotatably mounted within a housing, a drive means for rotating the drum, at least one hole through the wall of the drum, and an inlet to and outlet from the housing. 4. An atomiser as in Claims 3, wherein the drive means for the drum is a battery-driven electric motor. 5. An atomiser as in Claim 3 or Claim 4, wherein the electric motor and the battery are contained in a separate housing attached to or integral with the drum housing, with a drive shaft from the motor extending to the drum. 6. An atomiser as in any of Claims 2 to 5, wherein the means of containing the liquid has an outlet formed as, or to receive, a mouthpiece suited to be placed within the mouth of a patient. 7. An atomiser as in any of Claims 2 to 5, wherein an inlet to the means containing the liquid is provided. 8. An atomiser as in Claim 7, wherein the inlet is a strategically positioned opening in a wall of the means of containing the liquid. 9. An atomiser as in Claim 7, wherein the inlet is a strategically located permeabl sector of a wall of the means of containing the liquid. 10. An atomiser for liquids comprising a rotor, passageway means through the rotor terminating in an orifice means at the periphery of the rotor, means to supply liquid to the passageway means, drive means for the rotor, and means to enable droplets of liquid emerging from the orifice means to be entrained in a gas flow. 11. An atomiser as in Claim 10, wherein the rotor is formed by plate members suitably secured together, the inner surfaces of the plate members being structured such as to provide the passageways and the associated outlet orifice. 12. An atomiser as in Claim 10 or Claim 11, wherein the rotor is located in a chamber to provide a gas flow across the rotor. 13. An atomiser as in Claim 12, wherein the chamber serves as a sump for a liquid to be delivered to the rotor. 14. An atomiser as in any of Claims 12 or 13, wherein a drive means for the rotor is an electric mains or battery-driven motor located in a chamber attached to or formed integral with the gas flow chamber. 15. A method of providing an atomised liquid and an atomiser therefor substantially as hereinbefore described with reference to Figures 1 and 2 and Figures 3 and 4 of the accompanying drawings.

Inventors: ROWLAND STEPHEN JAMES, ROWLAND, STEPHEN, JAMES
Applicants: ROWLAND STEPHEN JAMES, ROWLAND, STEPHEN, JAMES
Application year: 1994
Main classification: A61M11
IPC codes: A61M11, A61M15, B05B3